The Cytological Diagnosis of a Malignant Effusion Is Independent of the Volume of Fluid Processed.

Abstract

Background: The relationship between pleural fluid volume and cytological diagnosis of malignancy has been often investigated with conflicting conclusions on whether or not a minimum fluid volume should be defined. The primary objective of this retrospective investigation is to evaluate the relationship between fluid volume and cytological diagnosis of malignancy.

Methods: A total of 511 body fluid specimen reports received between January 2018 and December 2019 were examined to investigate the relationship between diagnosis of malignancy to volume and biochemical properties. Pleural fluid (n = 252) and peritoneal fluid (n = 250) specimens were binned into two volume groups (< 75 mL, ≥ 75 mL). Pericardial fluid specimens (n = 9) were excluded due to small sample size.

Results: Prevalence of malignancy for pleural and peritoneal fluids was 20.2% and 20.08%, respectively, with no significant difference between the two volume groups. Malignant pleural effusions were associated with a serum to fluid protein ratio > 0.5 and malignant peritoneal effusions were associated with a serum ascites albumin gradient (SAAG) < 1.1 g/dL.

Conclusions: Our study did not find a significant difference in the diagnosis of malignancy between volumes ≥ 75 mL and < 75 mL in either pleural or peritoneal fluid. Fluid volume is, therefore, not an adequacy criterion for detecting malignancy in either pleural or peritoneal fluid. Our analysis on the biochemical properties of each malignant fluid type was supportive of current use of Light's criteria and SAAG for effusion fluid evaluation.